An aircraft's movement in flight is controlled by rotating the craft in its pitch, roll and yaw axes. Pitch is rotation around the lateral or transverse axis. This axis is parallel to the wings, thus the nose pitches up and the tail down, or vice-versa. An aircraft pitches up to climb and pitches down to dive. An aircraft increases or decreases the lift generated by the wings when it pitches up or down by increasing or decreasing the angle of attack (AOA) through the lateral axis. Roll is rotation around the longitudinal axis—an axis drawn through the body of the vehicle from tail to nose. Yaw is rotation about the normal axis—an axis perpendicular to the pitch and roll axes.
To control the pitch rotation of aircraft such as the Boeing 777, the pilots operate conventional “wheel-and-column” controls to manually command the elevators of the aircraft. A simplified diagram of conventional “wheel-and-column” controls in the flight deck is illustrated in FIG. 1 (a). To pull the airplane's nose up, e.g. during take-off or landing, the pilot would pull the column toward himself. Pushing the column away would do the opposite to the nose.
In a conventional elevator control, when the control column is pushed or pulled by the pilot, i.e. pilot commands, position transducers change the pilot commands to analog electrical signals. FIG. 1 (b) shows a simplified diagram of the pilot control and the elevator control unit. These signals are transmitted to a Flight Computer Electronics 240 (“FCE”), which uses the signals to compute the requisite control surface commands. The FCE 240 also uses airspeed data to calculate elevator feel commands, which are sent to a feel actuator 430 on the elevator feel unit 10. The feel actuator 430 supplies to the control column 12 a variable feel based on the airspeed. As is well-known to those skilled in the art, the variable feel unit 10 prevents the pilot from making unsafe pitch adjustments, by gradually stiffening the control column 12 at higher airspeed. The variable feel unit 10 also supplies a centering function that returns the control column 12 to a neutral position.
The conventional elevator variable feel control typically includes bi-directional hinge-type cam roller mechanisms. The bi-directional hinge mechanism typically utilizes compression springs, slotted cam roller and pivoting linkages to provide centering and variable feel functionality. The overall mechanism is complex, heavy, has backlash at neutral position, and offers little flexibility for tailoring the feel forces.
Therefore, it is desirable to have a less complex and light-weight variable feel unit for the elevator control.
It is also desirable to have a variable feel unit that can be customized or tailored for different feel forces.